U.S. Pat. No. 3,693,296 discloses a workpiece treating apparatus of the type which includes a plurality of centrifugal throwing wheels which are moveable into and retractable from a blast drum and blast cabinet. A cantilevered boom is provided for supporting the throwing wheels such that the throwing wheels are built integral with the boom and the boom is mounted on a boom car for support and mobility. Also built integral with the boom and supported by the boom car is the abrasive feed conveyor, including a drive means therefore, as well as a ventilating fan and duct work.
While the apparatus disclosed by U.S. Pat. No. 3,693,296 operates in a satisfactory manner, various features in its design can be improved. The cantilevered boom requires heavy structural design of the boom and boom car to resist deflection. Also, if additional or larger throwing wheels are used, thus extending the length of the boom, the supporting structure becomes excessively large. Further, the boom car supporting the cantilevered boom results in an increase of the space requirement for the total apparatus. Still further, support equipment (e.g., motor cooling blower, vent piping, abrasive gate solenoid valves and piping) must be mounted on the moveable boom car and thus requires flexible connections to plant utilities.